The present invention relates generally to ion implantation systems, and more specifically to an improved ion implanter linear accelerator energizing apparatus and system.
In the manufacture of semiconductor devices, ion implantation is used to dope semiconductors with impurities. A high energy (HE) ion implanter is described in U.S. Pat. No. 4,667,111, assigned to the assignee of the present invention, Eaton Corporation, which is hereby incorporated by reference as if fully set forth herein. Such HE ion implanters are used for deep implants into a substrate in creating, for example, retrograde wells. Implant energies of 1.5 MeV (million electron volts), are typical for the deep implants. Although less energy can be used, the implanter still must be capable of performing implants at energies between 300 keV and 700 keV. Eaton GSD/HE and GSD/VHE ion implanters can provide ion beams at energy levels up to 5 MeV.
Referring to FIG. 1a, a typical high energy ion implanter 10 is illustrated, having a in terminal 12, a beamline assembly 14, and an end station 16. The terminal 12 includes an ion source 20 powered by a high voltage power supply 22. The ion source 20 produces an ion beam 24 which is provided to the beamline assembly 14. The ion beam 24 is then directed toward a target wafer 30 in the end station 16. The ion beam 24 is conditioned by the beamline assembly 14 which comprises a mass analysis magnet 26 and a radio frequency (RF) linear accelerator (linac) 28. The linac 28 includes a series of resonator modules 28a-28n, each of which further accelerates ions beyond the energies they achieve from prior modules. The accelerator modules are individually energized by a high RF voltage which is typically generated by a resonance method to keep the required average power reasonable. The mass analysis magnet 26 passes only ions of appropriate charge-to-mass ration to the linac 28.
The linear accelerator modules 28a-28n in the high energy ion implanter 10 individually include an RF amplifier 50, a resonator 52, and an electrode 54 as schematically illustrated in FIG. 1b. The resonators, for example, as described in U.S. Pat. No. 4,667,111 operate at a frequency in the range of about 3-30 Mhz, with a voltage of about 0 to 150 kV, in order to accelerate ions of the beam 24 to energies over one million electron volts per charge state. A conventional connection of power between an RF amplifier 50 and a resonator 52 includes a first impedance matching network 56 within the amplifier 50 to match the active devices 51, which may be solid state or vacuum tube devices, to the transmission line 58 impedance, typically 50 OHMs. A second matching network 60 at the feed into the resonator 52 matches the transmission line impedance to the resonator load impedance. The power losses due to the matching networks 56 and 60, as well as the cable 58 are typically 2-5% of the total RF power. In addition, such matching networks and transmission lines or cables are costly. Further, the length of the cable 58 is critical, and an optimal cable length for matching purposes may include several meters of cable which occupies valuable space a in a typical high energy ion implantation system.
The present invention is directed to an integrated resonator and radio frequency (RF) amplifier system and apparatus for use in an ion accelerator, which eliminates or minimizes various problems associated with the prior art. In particular, the invention combines the previous multiple matching networks into a single network, thereby reducing the complexity and cost of an integrated resonator and RF amplifier system. The invention further provides a method of coupling an RF amplifier with a resonator.
In accordance with one aspect of the invention, an integrated resonator and amplifier system is provided wherein an RF output associated with the amplifier is substantially directly coupled to the resonator, thereby eliminating the costs associated with one or more matching networks and cables associated with prior art systems and devices. The system may comprise an amplifier having an RF output, a tank circuit substantially directly coupled to the RF output of the amplifier, and an accelerating electrode connected to the tank circuit. In addition to cost advantages, the present invention reduces the space required for an accelerator module. The present invention, moreover, eliminates or reduces the power losses associated with the eliminated networks and cable, thereby improving overall system efficiency. The reduction in the number of RF components according to the invention also advantageously improves the system reliability.
In accordance with another aspect of the invention, an apparatus is provided for accelerating ions in an ion implanter. The apparatus may comprise an amplifier having an RF output, a tank circuit having a coil substantially directly coupled to the RF output of the amplifier, and an electrode connected to the coil for accelerating ions.
In accordance with yet another aspect of the invention, a method of coupling an RF amplifier with a resonator in an ion accelerator is provided. The method comprises connecting an RF output of an amplifier to a coupler, and locating the coupler near a resonator coil, thereby coupling the RF output of the amplifier with the resonator. In addition, the invention provides for capacitive or inductive coupling of an RF amplifier with an ion accelerator resonator.